Mast structures of this type have become known from DE 197 10 556 C2, for example. They have an outer mast which is attached to the industrial truck and possibly can be tilted. The outer mast has two spaced columns which are interconnected by a lower and an upper traverse. An inner mast has spaced columns which are guided on the columns of the outer mast and are interconnected via a cross-beam or traverse at the upper and lower ends. The lower end mostly also has mounted thereon a cross-beam on which the so-called free lift cylinder is supported that actuates the load-carrying means which is guided to be movable height on the inner mast. Supported on the outer mast are two mast lift cylinders the piston rods of which are adapted to be connected to the upper cross-beam.
It is natural for the mast lift cylinders to move linearly. Here, it needs to be ensured that the cross-beam is always arranged horizontally during such displacing motion. Moreover, there must not be any superfluous space in the mounting between the piston rods and cross-beam. Tolerances cannot be avoided while the mast lift cylinders are manufactured and the lift structure is assembled. Thus, differences of several millimeters might happen to occur in the lift of the two mast lift cylinders with respect to the cross-beam that cannot be accepted, however. Therefore, it is known to make an appropriate adjustment during the pre-assembly of mast components and their final assembly. Shims have been used hitherto for this purpose that were fitted on the cross-beam during the mounting of the piston rods. The drawback of the known construction is that further setting work can be performed solely by detaching the piston rods from the cross-beam. This is time-consuming all the more so since it requires two adjustments, i.e. during the assembly of the lift frame and during the mounting of the lift frame on the truck.